1. Field
Apparatuses and methods consistent with exemplary embodiments relate to a ramp signal calibration apparatus and method and an image sensor including the ramp signal calibration apparatus.
2. Description of the Related Art
An image pickup device includes an image sensor. An image sensor is a semiconductor device that converts optical information into an electrical signal. Examples of the image sensor include a charge coupled device (CCD) image sensor and a complementary metal-oxide semiconductor (CMOS) image sensor.
A CMOS image sensor uses a column-parallel analog-to-digital conversion structure in order to improve power efficiency. An analog-to-digital converter (ADC) included in the CMOS image sensor is located in a small pixel column pitch. Therefore, a single slope analog-to-digital converter (SS ADC) and a two-step single slope analog-to-digital converter (TS SS ADC) may be used. The SS ADC is very small in size and has a high reliability. The TS SS ADC performs a coarse analog-to-digital conversion process for converting high-order bits and a fine analog-to-digital conversion process for converting lower-order bits in order to reduce the conversion time.